Underlord's Evil Soul.
Isaac stepped out of the crack and hurled forward as he tried to grab Underlord by his collar. But Underlord quickly placed walls of reality to protect him and thought they were enough to stop the white-haired man because they were nigh-indestructible.
"You fool, you are not a match for me!" Underlord roared into laughter. "I already broke my chains, and with the help of Erebus, I am already above level 800! You are nothing compared to me, and you came all the way here to just die!"
"Shut up, mortal." Isaac formed a fist and punched through reality. The walls broke like thin glass.
"Impossible!" Underlord cried out and was grabbed by his collar by a sturdy-looking hand. His mind screamed to escape because if he didn't escape right now, he would die!
"Escape!" Underlord shouted, and Isaac's hand strangely slipped off, as if it was coated with soap.